The invention relates to a method for determining the current filling level of a liquid, preferably a calibration, quality control, or cleaning medium, or waste water, in a container, for example of an analyzer, where an immersion pipe is dipped into the liquid in the container to be filled or drained, which immersion pipe is connected via a tube system to a pumping device and is subject to a gaseous medium, preferably air, where the pressure p in the tube system is measured.
There are a variety of known methods and devices which may be used to measure in different ways the level of a liquid in a container. Besides purely mechanical methods using floaters connected to display devices, there are various physical methods which determine the change of a physical parameter in a riser pipe or immersion pipe by means of a sensor. The sensors described are either in direct contact with the fluid (conductivity or resistance sensors, etc.) or have only indirect contact with the fluid (optical sensors, dielectric measurements, etc.) The disadvantage of all these methods or devices lies in the relatively high cost of the sensors, in their limited lifetime when they are in contact with a fluid, and in the fact that costs are prohibitive in the case of the one-way or one-time containers used in medical testing, for example.
Medical analyzers are sometimes furnished with devices which determine the amount or the level of a liquid in a container by accurately recording the volume of liquid moved, for instance via the pumping rate, and by storing this information in the analyzer. If standard containers with known initial filling levels are used the filling levels of individual containers may be determined from the stored data. The disadvantage here is that the system will only work reliably if the performance of the pumping or suction system may be considered constant over a prolonged period of time, which is not the case with most peristaltic pumps. Furthermore an exchange of partly filled containers between analyzers of the same type is not possible when this method is used.